1. Field of the Invention
The present invention relates to a contact development system in an electrophotographic imaging apparatus, and, more particularly, to a structure and method for referencing a developer roll to the photoconductive drum in a contact development system.
2. Description of the Related Art
In an electrophotographic imaging apparatus, such as a printer or copier, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over the surface thereof. An electrostatic latent image is formed by selectively exposing the uniformly charged surface of the photosensitive member. Microscopic marking particles, known as toner, are applied to the electrostatic latent image, and subsequently transferred to the media intended to receive the final, permanent image, which may be paper, an envelope, a transparency or the like. The toner image is fixed to the media by the application of heat and pressure in a fuser.
The application of toner to the electrostatic image on the photosensitive member is commonly referred to as developing or development, and the apparatus for applying the toner to the photoconductive drum or other photosensitive member is commonly referred to as a developing or development unit. The developing unit includes a housing having a compartment therein for containing toner, and a developer roll rotatably supported within the housing. A uniform layer of toner is applied to the developer roll by a supply roll or the like. In what is referred to as a contact development method, the developer roll is rotatably disposed in contact with the photosensitive member, and the developer roll applies a layer of toner directly to the surface of the photoconductive member.
In a contact development system, it is important to keep a constant nip force between the developer roll and the photoconductive drum over the entire length of the developer roll. Constant nip force ensures a uniform application of toner to the surface of the photoconductive drum. If the developer roll is not parallel to the photoconductive drum, the nip force along the developer roll varies, and the toner delivered to the photoconductive drum will not be uniform. Non-uniform application of toner to the photoconductive drum ultimately results in print quality defects.
It is known to support opposite ends of the developer roll on separate rollers mounted in the developer cartridge. The developer roll is spring biased against the photoconductive drum, even though the developer roll can float relative to the photoconductive drum surface. Referencing systems of this type can result in skew between the photoconductive drum and developer roll. Further, as the developer roll rides against the support rollers, the support rollers should rotate freely. However, friction can inhibit support roller rotation, causing uneven wear on the outer surface thereof. This is particularly problematic when, as commonly provided, the support rollers and/or pins mounting the support rollers are made of plastic or the like. Plastic components may deflect, causing skew. Plastic pins mounting the support rollers in the housing are often large in diameter, increasing rolling friction. Skew between the developer roll and the photoconductive drum, and friction in the support rollers are two major contributors to non-uniform nip forces between the developer roll and photoconductive drum. Occurrence of either can result in print quality defects.
The developer cartridge is a replaceable unit, having a life expectancy shorter than that of the base machine in which it operates. When properly operated, the support rollers do not wear excessively, and may not require replacement during the entire anticipated lifespan of the base machine. Therefore, providing the support rollers as part of the developer cartridge is wasteful, resulting in the unnecessary replacement thereof when the developer cartridge is replaced. Thus, needless expense is incurred.
What is needed is a referencing apparatus for a contact development system which minimizes or eliminates skew between the developer roll and photoconductive drum and which reduces friction in the rotation of developer roll support rollers.
The present invention provides a supporting, or reference structure for a contact development system, that references the developer roll to the same structure as the photoconductive drum, thereby eliminating a variable in the reference structure.
The invention comprises, in one form thereof, a photo imaging apparatus comprising a machine frame including a photoconductive member support assembly and a photoconductive member mounted in said photoconductive member support assembly. A developer cartridge includes a developer roll for applying toner to the photoconductive member. A developer cartridge support assembly includes a reference component mounted on the photoconductive member support assembly and a support component supporting the developer cartridge on the reference surface.
The invention comprises, in another form thereof a contact development system for applying toner to a photoconductive drum in an electrophotographic imaging machine, comprising a photoconductive drum support assembly and a developer cartridge including a housing and a developer roll rotatably mounted in the housing. A reference surface is provided in the photoconductive drum support assembly; and a developer cartridge support extends between the cartridge and the reference surface.
The invention comprises, in still another form thereof, a developer roll referencing apparatus for a contact developing system in an electrophotographic imaging machine having a machine frame and a photoconductive drum mounted in said machine frame. The development system includes a developer cartridge having a housing and a developer roll. The referencing apparatus comprises a reference surface in the machine frame, and a support body for the cartridge, the support body disposed on the reference surface.
The invention comprises, in a further form thereof, a method for referencing a developer roll to a photoconductive drum in a contact development system of an electrophotographic imaging machine. The method comprises providing a photoconductive drum support structure and a reference surface in the structure; providing a developer roll for rotation in contact with the photoconductive drum; urging the roll against the photoconductive drum; and supporting the roll by sliding engagement with the reference surface.
An advantage of the present invention is providing a common mounting component for the photoconductive drum and developer roll support rollers, which substantially reduces the potential for skew between the photoconductive drum and the developer roll, compared to mounting structures known heretofore.
Another advantage is providing a more stable mounting component for the developer roll support rollers.
Yet another advantage is eliminating the unnecessary replacement of developer roll support rollers by placing the support rollers in permanent structural frame components rather than in replaceable unit housings.